The international application WO 2012/028824 describes a filtering unit comprising at least two filter elements, each filter element having an internal face, an external face, a filtering mesh, two concentric circular edges, respectively an inner edge and an outer edge between which said filtering mesh extends, and radial ribs provided at least on the internal face, said radial ribs extending between said concentric edges and being distributed circumferentially in order to form distinct sectors on said internal face. Said filter elements are configured to be assembled against each other so that their respective internal faces face each other so as to define a space between them, wherein said radial ribs delimiting the sectors form circumferential compartments in said space. At least one of said inner edge and outer edge has passages respectively communicating with corresponding ones of the sectors. The filter elements are stacked along an axial direction between a first cover and a second cover.
By stacking a selected number of filter element pairs, a desired filter area is obtained for an intended application. Typically, the fluid for filtering penetrates into the stack via passages of the inner edge, passes through the filtering mesh, and, once purified, exits via other passages defined in the outer edge. Naturally, the flow of fluid through the filtering mesh could be reversed or arranged in some other way.
The filter described in that publication further comprises a divider arranged coaxially with the filter elements, the divider having distinct distribution columns, and a rotary backwashing distributor provided at the first cover. The rotary backwashing distributor has a shutter provided with a discharge opening and is mounted to rotate so that said discharge opening is periodically and selectively put into communication with each distribution column, whereby each distribution column periodically and selectively establishes communication between the discharge opening and respective ones of the passages.
In this way, periodically, the fluid flow is reversed in the sectors corresponding to passages in fluid communication with the discharge opening, which enables backwashing to be performed in these sectors due to the pressure gradient across the filtering mesh, i.e. the pressure gradient between the external face side and the internal face side. The fluid used for backwashing is then discharged through the discharge opening.
This filtering unit of the prior art comprises a distribution spacer forming part of the first cover. This distribution spacer has passages extending said distribution columns and the shutter is in sealing and sliding contact with an annular surface of the distribution spacer into which said passages open out. Furthermore, a distributor supporting structure, including a support having arms, is mounted on the first cover.
Now, a need has arisen for an improved distribution arrangement. One such need is the requirement for smaller filters. Therefore, there is a need for a new type of filtering units.